1.Field of the Invention
This invention relates to a peripheral bus switch that is adapted to connect together a pair of electrically independent peripheral buses to which arrays of peripheral devices are respectively coupled in a peripheral bus interconnect system to ensure continuous and uninterrupted access to all of the peripheral devices in the event that the peripheral bus controller which drives one of the peripheral buses should malfunction and require shut down.
2. Background Art
A conventional peripheral bus interconnect system is described while referring to FIG. 1 of the drawings. In the conventional bus system, at least first and second peripheral buses 1 and 3 are shown to which first and second arrays of peripheral devices (each designated PD0 . . . PD6) are respectively connected. By way of example, such peripheral devices may include a CD drive, a DVD drive, a hard disk drive, and the like. In the case of FIG. 1, each of the peripheral buses 1 and 3 is electrically isolated and driven independently from one another.
Access to and control of the peripheral devices connected to the first peripheral bus 1 is accomplished by means of a first primary peripheral bus controller 5. Access to and control of the peripheral devices connected to the second peripheral bus 3 is accomplished by means of a second primary peripheral bus controller 7. In the event that one of the primary peripheral bus controllers 5 or 7 should fail, then all of the peripheral devices PD0 . . . PD6 which are connected to the corresponding peripheral bus 1 or 3 cannot be accessed or used. Consequently, at least part of the peripheral bus system in which the defective peripheral bus controller is included cannot be operated which adversely impacts the overall system performance and efficiency.
In order to overcome the negative effects of a defective primary peripheral bus controller, it has been known to add back-up or redundant peripheral bus controllers to the peripheral bus interconnect system. As shown in FIG. 1, a redundant peripheral bus controller 10 is coupled to and connected in electrical parallel with the primary bus controller 5, while a redundant peripheral bus controller 12 is coupled to and connected in electrical parallel with the primary bus controller 7. In this regard, only one of the primary or redundant bus controllers 5 or 10 and 7 or 12 will be used to operate and access the peripheral devices connected to their respective independent peripheral buses 1 or 3.
To accomplish the foregoing, each of the primary and redundant peripheral bus controllers 5, 7, 10 and 12 is provided with its own isolation circuitry 14, 16, 18 and 20. The purpose of the isolation circuitry is to automatically isolate a defective primary bus controller 5 or 7 from its peripheral bus, whereby the defective primary bus controller will be disconnected from its companion redundant bus controller. The redundant peripheral bus controller 10 or 12 will then be connected directly to one of the independent peripheral buses 1 or 3 so that normal operation will resume to enable the peripheral devices to be accessible with essentially no interruption of service or performance degradation.
While the aforementioned solution of redundant peripheral bus controller 10 and 12 has been found to maintain system performance, new problems of costs and space consumption are introduced at the same time. That is to say, the end user will be subject to the considerable cost of having to add a back-up or redundant peripheral bus controller to be coupled to each primary peripheral bus controller. Moreover, there is often insufficient space in a storage enclosure to house all of the redundant peripheral bus controllers that are necessary to implement a fully fail-safe peripheral bus interconnect system. Consequently, the solution shown in FIG. 1 is not acceptable in every case.